Different in File Size & Size on Disk

I'm transferring files, from external hard disk to an another external hard disk...
from a non-external powered to an external powered one...

I'm using cut & paste...

Suddenly, blackout happens...

There'll be data writing failure...

So I checked some of my files(mostly in .iso)... Some of them have very big difference between Files Size & Size on Disk (around 4 GB)...

So, I tried to open it... Nothing happen...

Does this big difference can make anything goes wrong?

Are you talking about this?

Yup... but in your picture, the difference in not too big... but what happen to me is there value difference is about 4GB

iUnique said:

Yup... but in your picture, the difference in not too big... but what happen to me is there value difference is about 4GB

Click to expand...

lol...did you use winzip or winrar??

use PowerISO of course...

EDIT: Considering the power outage, try doing a chkdsk /f and see if it find errors, else you'll have to copy the files all over again.

-Original post by me:
Two possibilities: Compression using the default windows .zip interface and sector size. I would go with the latter. It's like this:

Compression is fairly easy to explain. "Size" dictates what the actual size is, and the "size on disk" dictates how much space it is occupying the hard disk after being squished in to a very small size.

Sectors are a bit more complicated. Your hard drive is divided in to many, many things. The smallest and most important are the sectors. Think of sectors as honeycombs in a bee's hive. They combine together to form an actual hive of honey.

Now, Windows 7 has a default sector size of 4KB. That means that for every block of data, it divides it into a 4KB pieces. Now if you have a 6KB file, the first 4KB will occupy sector 1. The next 2KB will occupy sector 2. You cannot add another file on sector 2 since it is already occupied by a file. Considering that, file 1 is actually occupying 8KB even though it is only 6KB.

To give you an example, I'll show you a screenshot of my PC. My sector size is at 32KB (the bigger, the better in performance )


See how even if it's 1 byte it takes up 32KB? It's because of my sector size.


That's a loss of 32,767 bytes. Of course, the effect stacks up. Now see what happens when I copy that file 237 times.



Hopefully that should give you a basic understaning on why there's a big difference on "Size" and "Size on disk".

Durning the copy process, Windows probably made sparse files to pre-allocate large block for the file to be written to. Which might accound for the difference.

iUnique said:

I'm transferring files, from external hard disk to an another external hard disk...
from a non-external powered to an external powered one...

I'm using cut & paste...

Suddenly, blackout happens...

There'll be data writing failure...

So I checked some of my files(mostly in .iso)... Some of them have very big difference between Files Size & Size on Disk (around 4 GB)...

So, I tried to open it... Nothing happen...

Does this big difference can make anything goes wrong?

Click to expand...

You had a power failure...

The file is incomplete on your destination disk and yes the size difference matters *A LOT*. What you should do is delete the incomplete file and copy it over again.

You had a power failure...

The file is incomplete on your destination disk and yes the size difference matters *A LOT*. What you should do is delete the incomplete file and copy it over again.

Click to expand...

But the prob is, I was moving the file, not copying the file... when I checked back the original hard drive, the file is gone.. but it present in the destination hard drive... have same file size (as what I have remembered)... But I'm getting suspicious about the file size & size on disk... By the way, the file is .iso, when I opened it with PowerISO, I get no error message... It means that there's no prob at all, am I right?

So, the file is actually normal, right?

why you not try use other...dont use powerISO..

compare it.

iUnique said:

But the prob is, I was moving the file, not copying the file... when I checked back the original hard drive, the file is gone.. but it present in the destination hard drive... have same file size (as what I have remembered)... But I'm getting suspicious about the file size & size on disk... By the way, the file is .iso, when I opened it with PowerISO, I get no error message... It means that there's no prob at all, am I right?

So, the file is actually normal, right?

Click to expand...

That's very hard to say... If it's an ISO see if PowerISO can extract it without error... merely opening it only verifies the internal directory.

If you can confirm the file is OK... then the disparity in size and disk usage is not a problem... Simply defragment the disk.

arkhi said:

EDIT: Considering the power outage, try doing a chkdsk /f and see if it find errors, else you'll have to copy the files all over again.

-Original post by me:
Two possibilities: Compression using the default windows .zip interface and sector size. I would go with the latter. It's like this:

Compression is fairly easy to explain. "Size" dictates what the actual size is, and the "size on disk" dictates how much space it is occupying the hard disk after being squished in to a very small size.

Sectors are a bit more complicated. Your hard drive is divided in to many, many things. The smallest and most important are the sectors. Think of sectors as honeycombs in a bee's hive. They combine together to form an actual hive of honey.

Now, Windows 7 has a default sector size of 4KB. That means that for every block of data, it divides it into a 4KB pieces. Now if you have a 6KB file, the first 4KB will occupy sector 1. The next 2KB will occupy sector 2. You cannot add another file on sector 2 since it is already occupied by a file. Considering that, file 1 is actually occupying 8KB even though it is only 6KB.

To give you an example, I'll show you a screenshot of my PC. My sector size is at 32KB (the bigger, the better in performance )


See how even if it's 1 byte it takes up 32KB? It's because of my sector size.

That's a loss of 32,767 bytes. Of course, the effect stacks up. Now see what happens when I copy that file 237 times.

Hopefully that should give you a basic understaning on why there's a big difference on "Size" and "Size on disk".

Click to expand...

Very informative arkhi!

How could you change the sector size?

Jonathan_King said:

Very informative arkhi!
How could you change the sector size?

Click to expand...

You cannot change the sector size of the disk that's hard-coded at the factory.
Currently hard disk sectors are 512 Bytes. The new Advanced format disks will be 4k sectors.

You CAN change the cluster size (number of sectors per allocation unit) when you format...


Moreover; larger cluster sizes do NOT give better performance... they simply waste disk space.

CommonTater said:

Jonathan_King said:

Very informative arkhi!
How could you change the sector size?

Click to expand...

You cannot change the sector size of the disk that's hard-coded at the factory.
Currently hard disk sectors are 512 Bytes. The new Advanced format disks will be 4k sectors.

You CAN change the cluster size (number of sectors per allocation unit) when you format...


Moreover; larger cluster sizes do NOT give better performance... they simply waste disk space.

Click to expand...

Oops, forgot I confused clusters with sectors. Anyway, they DO increase performance, more especially on a setup with huge files. I believe the most should be at 32k as 64k would be too much.

@Jonathan_King
You have to do it at initial setup via command prompt with diskpart or "format /a:32k"